Method for the manufacture of chromic oxide



H. C. ROTH Sept. 17, 1929.

METHOD FOR THE MANUFAGTURE OFy CHROMIC OXIDE Filed May 12. 1927 Patented sept. 17, 192e HERMANN C. ROTH, F DORMONT, PENNSYLVANIA Y. METHOD FOR THE MANUFACTURE OF CHROMIC OXIDE Application filed May 12,

My invention relates to a method for they manufacture of chromi'c oxide from an alkali bichromate.,

@ne object of my invention is to provide a method of making chromic oxide in an airtight retort.

Another object of my invention is to provide a method of making chromic oxide by an exothermic reaction in the presence of a reducing substance without thev application of external heat.

Another object of my invention is 'to' provide a method for improving the quantity of chromic oxide made by utilizing unleached chromic oxide as an insulating medium during the making' of chromic oxide'from an alkali bichromate. f

Another object of my invention is to provide a method for making chromic oxide'that utilizes the heat of reaction of a portion of a charge for heating the major p'ortipn of the -charge to reaction temperature.

Another object of my invention is to provide a method for making chromic oxide that utilizesthe heat of reaction of a charge of alkali bichromate for volatilizing a reducing agent, such as sulphur. f

At the present time chromic oxide (C1303) is manufactured from an alkali bichromate the presence of 'a reducing agent such as sulphur or carbon, or a mixture of both, ina horizontal muile furnace heated to a temperature ofabout 600 to 700 degrees C. Theoretically, the amount of the. reducing agent applied to the mixture is such that none of it should be free after the reaction has taken place. However, as a practical expedient, it has been found advisable to add a considersuch as sodium or :potassium bichromate in able amount of a reducing agent in excess of' 1927. Serial No. 190,717.

is drawn through the furnace during the reaction which escapes into the adjacent atmosphere with ,thel loss of a considerable amount of sulphur and resulting in an incomplete chemical reaction. Thermo-chemical calculationspshow that the reaction of sodium or potassium bichromate with sulphur 1s an exothermic reaction and that, when'once initiated, the heat resulting'is suficient to raise the temperature of the substances to the temperature required for reactlon and also to volatilize any reasonable excess of sulphur present.

Accordingly, I provide a closed retort in which is inserted a charge of alkali bichromate and sulphur which is initially ignited, 'I hereater the reaction takes place with the liberation of a considerable quantity of heat and the expansion of the charge to substantially twice its initial volume. Since the retort is closed, no sulphur vapors escape therefrom and no outside air is drawn into the retort to hinder a complete chemical reaction. The sulphur vapors are conducted to a con- (lensing apparatus where they are precipitated either in a solid or liquid condition as may be desired. The .condensingwapparatus mayalso be connected to a source of inert gas such that the latter fills the condensing apparatus as the pressure therein drops during the condensation process.

The accompanying drawing is av diagrammatic illustration of an embodiment of my invention and is not to be considered a limitation thereof, as it is obvious-that the invention may be practicedin other apparatus.

In the accompanying drawings: Figure 1 is a view, partially in elevation and partially in section, of a diagrammatic embodiment of my invention;

Figure 2 is a sectional view of a detail of my invention; and

Figure 3 is a similar 'view of a further modification of my invention. i 9o Referring to Figure 1, my apparatus may comprise in general a retort 2 mounted on a hydraulic jack 3 for cooperation with a cupolaI 4.J connected by a pipe line 5 to a condensingapparatus 6 that in turn is connected 100 by a pipe line 7 through a reducing valve 8 to a source 9 of inert gas.

The retort 2 may be of any suitable size and shape, and-preferably lined with refractory material, depending upon the volume of the charge 11 of bichomate and reducing agent.

An insulating lining or `layer 12 of chro mic oxide is tilled in around the walls otthe. 'retort 2 to serve as a heat insulatingmedium for the Walls of the retort and to prevent the sticking ot the charge to the retort walls during its reaction. It the unwashed substance resulting from a previous operation is use d for making up the layer 12, any alkali bichromate that may have remained therein will have an opportunity' to be converted into chromic oxide as this unlea-ched substance,A

while mainl intended as a heat insulator, actually un ergoes a second reaction. A heater 13 may be inserted in the Wall ot the retortl and subjected to a flame 14 for raising the temperature fg@ the charge adjacent thereto above the ignition point.v As

soon as't'he Vignition point of the charge is reached and the exothermic reaction takes place, the heater 13 may bewithdrawn and the opening through which it 1s inserted sealed up.

The jack 3 may be of any suitable type,

. and as herein shown is of the hydraulic type with a plate controlled by inlet and outlet valves 15 and 16, respectively. A plunger 17 is provided 18 on which therretort 2 1s mounted. The stroke of the plunger 17 is such that the retort 2 is moved upwardly into tight engagement with the cupola 4.

The cupola/l maybe supported by a suitable structure comprising angle irons 19 and is provided With an opening' 21 normally closed by a valve 22 that may be operated by a handle 23 extending through a housing 24. The pipe line 5 is connected from the housing 24 to the condensing chamber 6.

The condensing apparatus 6 is provided vWith a door 25-l through Which the condensed sulphur 26 may be removed. The.'

reducing valve 8 is provided for supplying an inert gas such as nitrogen orcarbon dioxide from the container 9 to the`-con densing apparatus 6 when the pressure in the 'latter falls -below "a predetermined amount during the period of condensation. l

bichromate. such as' crystallized chromate, is as follows:

sodium bi- WVith potassium bichromate the equation is iKzCrzO' S =K2SO4+ Craoa- According to the foregoing equations, no free sulphur should be present at the conclusion of the reaction. However, av better chemical reaction is had when an excess of sulphur vis added to the charge 11. Such sulphur and Water as may be present are volatilized during the exothermic .reaction and pass-through the opening 21 and the pipe line 5 to the condensing apparatus 6, leaving a solid sodium sulphate (NazSOQ and chrome Oxide (CrZOJS) in the retort. After the react-ion is completed the valve 2 2 is closed, the retort 2 lowered by the jack 3 and emptied. The retort 2 may then be filled for a subsequent operation. The sodium sulphate may be separated from the chromic oxide by a number of methods one of which is that of dissolving or leaching out the sodium sulphate.

The speed of the reaction may be retard- Nazisogcrzogfznzo ed in a number ot'ways such as the addition of Water in a free state or as adherent moisture, or as water of crystallization. The amount of excess sulphur volatilized absorbs heat and accordingly the rate otl of surplus sulphur added and by the size of its grains. ln order to accelerate the reaction, tine grained material may be intil) mately mixed with the Charge.

Referring to Figure 2, I havey shown a retort 2 in whichl provision is made for igniting the charge by the insertionof a hot metallic rod 27. l

In Figure 3 ll have shown a form of my inventiony in which an electrical arc is produced by aspark plug 28 in thepresence ot' thermite 29 or other highly combustible chemical substances in order to fire the charge 11. lt is to be understood that the 4sparli plug 12 represents one tpe 0f der' vice for producing an electrica arc,r and that other types of electrical arcs may be substituted therefor. In all of the modifications of the invention it is desirable that the' ignition apparatus be Withdrawn from the interior of the retort 2 during the exothermic reaction. 'i

Accordingly, I have devised a method and apparatus for the manufacturev of chromic oxide characterized by the insertion oflan alkali bichromate, which term is used generically to include both an alkali metal bichromate and a ynon-metal alkali bichromate such as ammonium bichromate, and a reducing agent, preferably sulphur, into a closed retort, igniting the charge and then vreaction may be controlled bv the quantity permitting an exothermic action to take place during which the excess of sulphur is volatilized and passed over to a condensf ing chamber. This method of making chromic oxide is advantageous in that air is prevented from entering the retort during the chemical reaction, thereby retarding the chemical reaction, and passingr sulphur fumes into the atmosphere with, the

consumption of an unnecessarily large amount of fuel expended in heating 4Aa muiile. n

It is to be understood that various changes may be made in the size, shape `and disposition of the component parts of the apparatus'as shown and inthe manner of applying them to the method of manufacturing chromic oxide, such as the use of a horizontal Inuiiie and a movable cupola, as well as the steps in the method, withoutdeparting from the scope of-.theappended claims.

I claim:

1. In the methodof making chromic oxide from an alkali vbichromate, the steps consisting in igniting in the absence vof any l oxidizing agent other than the bichromate a my hand.

HERMANN c. ROTH. 

